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When using patchable-function-entry, the compiler will record the
callsites into a section named "__patchable_function_entries" rather
than "__mcount_loc". Let's abstract this difference behind a new
FTRACE_CALLSITE_SECTION, so that architectures don't have to handle this
explicitly (e.g. with custom module linker scripts).
As parisc currently handles this explicitly, it is fixed up accordingly,
with its custom linker script removed. Since FTRACE_CALLSITE_SECTION is
only defined when DYNAMIC_FTRACE is selected, the parisc module loading
code is updated to only use the definition in that case. When
DYNAMIC_FTRACE is not selected, modules shouldn't have this section, so
this removes some redundant work in that case.
To make sure that this is keep up-to-date for modules and the main
kernel, a comment is added to vmlinux.lds.h, with the existing ifdeffery
simplified for legibility.
I built parisc generic-{32,64}bit_defconfig with DYNAMIC_FTRACE enabled,
and verified that the section made it into the .ko files for modules.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Helge Deller <deller@gmx.de>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Torsten Duwe <duwe@suse.de>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: Sven Schnelle <svens@stackframe.org>
Tested-by: Torsten Duwe <duwe@suse.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James E.J. Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: linux-parisc@vger.kernel.org
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This patch implements dynamic ftrace for PA-RISC. The required mcount
call sequences can get pretty long, so instead of patching the
whole call sequence out of the functions, we are using
-fpatchable-function-entry from gcc. This puts a configurable amount of
NOPS before/at the start of the function. Taking do_sys_open() as example,
which would look like this when the call is patched out:
1036b248: 08 00 02 40 nop
1036b24c: 08 00 02 40 nop
1036b250: 08 00 02 40 nop
1036b254: 08 00 02 40 nop
1036b258 <do_sys_open>:
1036b258: 08 00 02 40 nop
1036b25c: 08 03 02 41 copy r3,r1
1036b260: 6b c2 3f d9 stw rp,-14(sp)
1036b264: 08 1e 02 43 copy sp,r3
1036b268: 6f c1 01 00 stw,ma r1,80(sp)
When ftrace gets enabled for this function the kernel will patch these
NOPs to:
1036b248: 10 19 57 20 <address of ftrace>
1036b24c: 6f c1 00 80 stw,ma r1,40(sp)
1036b250: 48 21 3f d1 ldw -18(r1),r1
1036b254: e8 20 c0 02 bv,n r0(r1)
1036b258 <do_sys_open>:
1036b258: e8 3f 1f df b,l,n .-c,r1
1036b25c: 08 03 02 41 copy r3,r1
1036b260: 6b c2 3f d9 stw rp,-14(sp)
1036b264: 08 1e 02 43 copy sp,r3
1036b268: 6f c1 01 00 stw,ma r1,80(sp)
So the first NOP in do_sys_open() will be patched to jump backwards into
some minimal trampoline code which pushes a stackframe, saves r1 which
holds the return address, loads the address of the real ftrace function,
and branches to that location. For 64 Bit things are getting a bit more
complicated (and longer) because we must make sure that the address of
ftrace location is 8 byte aligned, and the offset passed to ldd for
fetching the address is 8 byte aligned as well.
Note that gcc has a bug which misplaces the function label, and needs a
patch to make dynamic ftrace work. See
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90751 for details.
Signed-off-by: Sven Schnelle <svens@stackframe.org>
Signed-off-by: Helge Deller <deller@gmx.de>
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